The amelioration of degraded larch(Larix olgensis)soil depends on the proportion of Aralia elata litter in larch-A.elata agroforestry systems

Research has indicated that introducing Aralia elata into larch plantations forms an agroforestry system which could provide economic benefi ts for local farmers and improve degraded soils.However,the impact of litter mixtures on soil chemical and microbial properties in this agroforestry system are unclear,which limits effi cient management of the agroforestry system.A 365-d incubation experiment examined the eff ect of litter mixtures of diff erent proportions of larch(L)and A.elata(A)on soil chemical and microbial properties.The results show that levels of mineral N,available P,microbial biomass carbon and nitrogen,cumulative C mineralization,and activities of hydrolases and oxidases increased with an increase of A.elata in the litter mixtures.Concentration of total soil carbon,nitrogen,and phosphorous did not change(except for total nitrogen).Compared with larch litter alone,levels of mineral N,available P,microbial biomass carbon and nitrogen,cumulative C mineralization,and the activities of hydrolases and oxidases increased by 7.6–433.5%.Most chemical and microbial properties were positively correlated with mixed litter proportions and the initial levels of N,P,K,Ca,Mg,Mn,Zn and Cu in the litter,while negatively correlated with the initial concentrations of C,Fe and lignin,C/N and lignin/N ratios.The results indicate that A.elata litter can improve degraded larch soil and the degree depends on the proportion of A.elata litter in the litter mixtures.

Impacts of soil properties on phosphorus adsorption and fractions in purple soils

Information on phosphorus(P) adsorption and its impacts on the redistribution of the P fraction in soil profiles are important for environmental management under intensive agricultural practices.To clarify the dominant factors influencing soil phosphorus adsorption in an Entisol(locally known as purple soil), P adsorption experiments were conducted in Sichuan Basin of southwestern China for cropland and woodland soils with acidic, neutral and calcareous origins throughout their profile. After various doses of P were added during incubation experiments, soil P fractions were also analyzed. The results showed that there were no significant differences in Fe-oxides and P adsorption along the vertical gradients. Agricultural practices and lower p H conditions reduced the P adsorption capacity of purple soils throughout the soil profiles. For acidic and neutral purple soil profiles, the P adsorption capability was mainly influenced by Fe-oxides and soil texture. Ca-bound P and Fe-Al-bound P represented the majority of the total inorganic P of calcareous soils.There was a saturation of adsorption capacity by sesquioxide and a high risk of dissoluble reactive P(NH_4 Cl-P) being released out of the soil profile in acidic and neutral purple soils after the greatest P addition, indicated by the higher proportions of NH_4 Cl-P(over 40%) and decreasing Fe-Al-P fraction.P fractions migrated with greater difficulty in calcareous purple soil profiles as Ca-P fraction peaked over 65% when adding a P dose at or greater than 80 g P kg^(-1), indicating the high potential of P adsorption.The X-Ray Diffraction analysis also verified the formation of brushite. Adaptive management practices should be designed to alleviate P losses for acidic and neutral purple soils.

Short-Term and Long-Term Effects of Natural and Artificial Carbonaceous Substrates on Greenhouse Gas Fluxes

The emissions of two greenhouse gases(GHG),carbon dioxide(CO_(2))and nitrous oxide(N2O),from six substrates with different carbonaceous content were compared in short and long-term incubation experiments.Three natural soils and three artificial chars were mixed with carbon(C)poor soil(Cambisol)to simulate real conditions after application of char to farmland.The natural soils were a Cambisol,an Anthrosol and a Histosol with C contents of 1.3%,4.4%and 13.2%,respectively.The three chars produced through thermal conversion of wood chips by hydrothermal carbonisation(HTC),fluidized bed gasification and pyrolysis had C contents of 56.9%,75.4%and 79.9%,respectively.Emission rates of CO_(2)and N2O from the rewetted substrates were measured by gas chromatography over a short time of 72 h and over a long period of nearly two years.The short-term CO_(2)emissions from the natural soils showed a clear relationship to their C content.The emission rate for the Histosol/Cambisol mixture was three times higher than that for the pure Cambisol,77.1 vs.23.5 mg CO_(2)-C kg^(-1)organic matter(OM)per hour.The C emission rates for the char/Cambisol mixtures were much lower,ranging between 3.0 and 9.1 mg CO_(2)-C kg OM^(-1)h^(-1),and did not correspond to their total C contents.Comparison between the two incubation lengths showed that the long-term CO_(2)emission rates were generally one order of magnitude lower than the short-term rates.The final emission rates for natural substrates over a period of two years were still twice those for artificial char substrates,between 2.2–3.5 mg CO_(2)-C kg OM^(-1)h^(-1)and 1.3–1.8 mg CO_(2)-C kg OM^(-1)h^(-1),respectively.Although the contents of total nitrogen(Ntot)and extractable nitrogen(Nmin)were considerable in the chars under study,enhanced N2O release was not observed in the incubation experiments.Instead,N2O emission rates in the three mixtures of chars and Cambisol were lower by one to two orders of magnitude compared to the pure Cambisol in short-term incubations.Even long-term N2O emissions were 5 to 9 times lower.The highest degree of N2O reduction was found for the HTC char.Because of the high global warming potential of N2O,this positive effect of chars may play an important role in mitigating emissions of CO_(2)equivalents.Both CO_(2)and N2O must be taken into account when balancing GHG emitted after chars(biochar,gasifier char,HTC char)are applied to soil.